The invention relates to dissolving barium sulfate solids from locations in and around the boreholes of wells and/or other relatively remote locations into which a fluid can be flowed.
Various well treating procedures for removing various types of scales with aminopolyacetic acid salt chelating agents, such as EDTA (ethylenediaminetetraacetic acid), are known. For example, U.S. Pat. No. 2,396,938 (filed in 1944) describes removing boiler scale with aqueous solutions of such a chelant and an alakali metal hydroxide. U.S. Pat. No. 2,802,788 (filed in 1952) describes a radiator cleaning composition in which such a chelant salt is included in an aqueous solution along with an inorganic chelant, e.g., sodium tripolyphosphate. U.S. Pat. No. 3,308,065 (filed in 1963) describes a substantially one-pore volume treatment for removing calcium sulfate-containing scale with an ammoniated or aminated chelant, e.g., an ammonium salt of EDTA. U.S. Pat. No. 3,660,287 (filed in 1967) describes a similar treatment for dissolving calcium sulfate-containing scale with a mixture of an EDTA salt and water soluble inorganic carbonate salt. While the above processes were consistent in utilizing an amount of solution which about filled one pore volume of the region within which the scale was to be removed and using a concentration of chelant such that that volume of the solution contained a stoichiometric excess relative to the amount of scale to be dissolved, U.S. Pat. Nos. 2,877,848 and 4,030,548 relate to using relatively dilute solutions. The U.S. Pat. No. 4,030,548 patent describes the tendancy for relatively concentrated EDTA solutions to become quickly saturated with a Ba-EDTA complex and suggests a once-through-dynamic wash treatment with enough solution to gradually remove the solid.
Numerous monocyclic and bicyclic macrocyclic polyethers and their tendancies to chelate with alkaline earth metals and to dissolve salts of such metals are disclosed in "Tetrahedron Letters" No. 34 (1969), pages 2889-2892. U.S. Pat. Nos. 3,888,877 and 3,966,766 relate to such polyethers and their general utility as chelating agents.
Our co-pending patent application Ser. No. 951,701, filed Oct. 16, 1978, relates to dissolving a barium sulfate solid from a remote location into which fluid can be flowed by contacting that solid with an aqueous solution consisting essentially of: water, a bicyclic macrocyclic polyether, a proportion of alkali metal salt of an organic acid which is less than that of the polyether but is sufficient to catalytically increase the rate of barium solid dissolving by the polyether, and enough dissolved alkaline inorganic alkali metal or ammonium compound to provide a solution pH of at least about 8.